Our recent findings show that morphine inhibits milk-ejection, presumably by interfering with OT release in lactating mice (12). Our preliminary results demonstrate that beta-endorphin also inhibits OT release. We do not, however, known how they exert their inhibitory actions. We thus wish to determine the mechanism by which morphine and beta-endorphin inhibit OT release. We would also like to establish the cause for stress-induced inhibition of OT release. Finally, we wish to solve the controversial issue whether the antidiuresis following morphine administration is due to ADH release or not. If it is then what is the site of action of morphine? Actions of morphine and of beta-endorphin on OT release will be tested in vivo and in vitro. Experiments in vivo will be designed so that the hormone release can be estimated by target organ responses as well as by direct estimation in blood. The effects of intraventricular morphine and of beta-endorphin on OT release in response to intraventricular Ach will be tested in lactating rats. Hormone level in blood will be detected in lactating rabbits. In vitro experiments will be done on isolated neural lobes, isolated hypothalamic nuclei and on entire hypothalamo-hypophysial system from rats. Effect of morphine will be tested on all three above preparations and of beta-endorphin on some selected preparations. Hormone release in vitro preparations will be estimated by RIA. Our in vitro experiments will give us information about the site of action of morphine and of beta-endorphin and to some extent about the mechanism of action. Detection of ADH release by morphine both in vivo and in vitro experiments will be estimated by RIA.